Composition for the treatment of steel



United States Patent Office 3,410,681 Patented Nov. 12, 1968 3,410,681 COMPOSITION FOR THE TREATMENT OF STEEL Nicholas Orb-an, Paris, France, assignor to Anstalt fur Technische Entwicklung und Verwertung, Vaduz, Liechtenstein, an establishment of Liechtenstein No Drawing. Filed Sept. 28, 1965, Ser. No. 491,040

7 Claims. (Cl. 75-94) H ABSTRACT OF THE DISCLOSURE I disclose, a composition for-the treatment of steel to eliminate flaws and defects in the steel comprising a mixture of sodium carbonate, calcium fluoride and a saponifiable fatty acid capable of reacting with the sodium carbonate and calcium fluoride to produce a foamy slag capable of uniformly covering liquid steel.

oxygen on the steel when the steel is poured in the form of a stream from the ladle into the ingot mold (or other mold). This chemical action is magnified by the large surface of steel in the stream which is exposed to the oxygen in the air. During pouring the steel stream breaks in droplets which will be oxidized on the surface. These oxidized droplets are not dissolved in the steel of the ingot and will not weld to the ingot. The oxidized droplets may adhere -to the wall of the mold and become encrusted in the skin of the ingot or other casting forming inclusions which are the origin of serious flaws which appear when the ingot is rolled.

Other defects are due to the presence in the steel of elements introduced during melting or refining of the steel to calm or kill the steel by eliminating dissolved oxygen. Such elements (for example, Si, Mn, Al, Ti, etc.) are more oxidizable than iron and cause the elimination of the dissolved oxygen in the steel by chemical reaction with the dissolved oxygen to form oxides. It is known that the chemical afiinity of such elements for oxygen increases rapidly during the cooling and solidification of the steel so that they are the origin of the presence in the steel of inclusions which solidify generally before the steel itself solidifies. Such inclusions are incapable of rising to the surface of the ingot because of the rapid increase in the viscosity of the steel due to cooling and are seriously detrimental to the quality of the finished product.

Attempts have been made to solve the problem but prior to the present invention such attempts have not been entirely successful. For example, in order to do away with surface flaws, various suitable compositions have been deposited on the walls or the bottom of the ingot mold, but in all cases it is necessary to clean the ingot or slab with a torch after its production (scarfing). Attempts have also been made to eliminate or reduce the oxidation occurring at the time of casting by avoiding or restricting contact of the stream of liquid steel with the air as by casting under vacuum or in a neutral gas atmosphere, but such methods require a costly and complicated installation which cannot be used for casing ingots in series.

An object of the invention is to provide a simple and effective solution to the problem above explained.

The use of sodium carbonate and of calcium fluoride in the treatment of steel is known to those skilled in the art. I utilize sodium carbonate and calcium fluoride in a composition for the treatment of steel but provide for perfecting or improving such composition so as to ob.- tain the desired result.

' My invention may be practiced in one of its aspects in the treatment of steel to eliminate defects resulting from the oxidation of the steel or from the presence of deoxidizing elements in the steel by adding my composition to the steel in diflerent ways: (1) when tapping from the furnace into the ladle, (2) in the ladle itself or (3) when pouring or teeming from the ladle into the mold. My composition comprises a mixture of sodium carbonate, calcium fluoride and organic acid. The organic acid normally exists in liquid to solid state. The mixture may include one or more substances designed specifically to deoxidize the steel.

Among the substances that can be used in my composition for the treatment of steel to eliminate flaws and defects in the steel are fatty acids. I may employ stearic acid (or commercial stearin, which is a mixture of fatty acids) and/or tartaric acid. Polyfunctional acid may be employed.

The action of my composition on the steel is both physical and chemical. The physical action. is a modification of the surface tension of the mixture of sodium carbonate and calcium fluoride. It is known that the addition of sodium carbonate and calcium fluoride to liquid steel results in formation of a thick more or less liquid slag which is distributed non-uniformly on the surface of the steel and which forms poorly distributed agglomerates. The resulting discontinuity does not, therefore, prevent oxidation of the surface of the steel. The presence of the aforementioned components of my composition modifies the surface tension so that the slag is foamy and covers the liquid steel uniformly.

The foam results from chemical reaction between the stearic acid and/or tartaric acid or equivalent material present in the mixture and the sodium carbonate with formation, by saponification, of stearate and/or tartrate of soda and of carbon dioxide gas. The stearate and/or tartrate of soda which is formed dissolves partially, emulsifying the calcium fluoride and thus creating a foamy and partially volatile slag. The vapors of stearate and/or tartrate of soda mixed with the carbon dioxide gas liberated by the reaction fill up the ladle or mold and thus exclude atmospheric air, thus preventing oxidation of the steel by the oxygen of the air during casting.

Moreover, when my composition is introduced combustion takes place which fixes the oxygen initially present'and thus opposes any initial oxidation.

A secondary effect is the liberation of carbon dioxide in the form of bubbles in the midst of the mass of liquid steel. The inclusions formed during the solidification of the steel by reason of the increasing afiinity of the deoxidizing elements initially present for the dissolved oxy-- gen are brought to the surface by the buoyant effect of the bubbles. Such inclusions then become part of the continuous slag resulting from the modification of surface tension. The slag also will penetrate between the ingot or other casting and the mold wall creating a protective coating therebetween.

Another possibility of utilization of my composition is in the production of rimmed or semi-killed steel. The chemical reaction between the organic acid and the sodium carbonate liberates carbon dioxide and this carbon dioxide is useful as a rimming agent by increasing the skin thickness of the ingot. The presence of the organic acid will accelerate the liberation of carbon oxide and the free flowing foamy slag will distribute better the rimming agent. The coating action stays the same as mentioned above.

I prefer to add my composition to the steel gradually during the casting of the ingot. However if desired it may be added in the casting ladle itself, preferably immediately before casting or teeming into the ingot mold. The amount of my composition employed may vary within fairly wide limits, for example, between one ounce and ten pounds per ton of steel.

I have found the mixture of sodium carbonate, calcium fluoride and stearic acid and/ or tartaric acid to be particularly effective. The components should be employed in the following proportions:

Percent Sodium carbonate -60 Calcium fluoride 20-60 Stearic acid and/or tartaric acid 10-70 Preferred ranges are:

Percent Sodium carbonate 10-40 Calcium fluoride 20-60 Stearic acid and/or tartaric acid 10-50 A composition which I have found to be particularly effective is:

Percent Sodium carbonate 23 Calcium fluoride 44 Stearic acid and/or tartaric acid 33 While I have described certain present preferred embodiments of my invention and certain present preferred methods of practicing the same it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

I claim:

1. A composition for the treatment of steel to eliminate flaws and defects in the steel comprising a mixture of sodium carbonate, calcium fluoride and a saponifiable fatty acid capable of reacting with the sodium carbonate and calcium fluoride to produce a foamy slag capable of uniformly covering liquid steel.

2. A composition for the treatment of steel to eliminate flaws and defects in the steel comprising a mixture of sodium carbonate, calcium fluoride and stearic acid.

3. A composition for the treatment of steel to eliminate flaws and defects in the steel comprising a mixture of the following listed components in the percentage ranges indicated:

Percent Sodium carbonate 10-60 Calcium fluoride 20-60 At least one of the group consisting of stearic acid and tartaric acid 10-70 4. A composition for the treatment of steel to eliminate flaws and defects in the steel comprising a mixture of the following listed components in the percentages indicated:

Percent Sodium carbonate 23 Calcium fluoride 44 At least one of the group consisting of stearic acid and tartaric acid 33 5. A method of treating steel comprising adding to molten steel at a selected time between the conveying of the steel to the casting ladle and the casting of the steel into an ingot mold a quantity of the composition comprising a mixture of sodium carbonate, calcium fluoride and a saponifiable fatty acid.

6. A method of treating steel comprising adding to the molten steel at a selected time between the conveying of the steel to the casting ladle and casting the steel in the mold a quantity in the range of 1 ounce to 10 pounds per ton of steel of the composition comprising a mixture of sodium carbonate, calcium fluoride, and a saponifiable fatty acid.

7. A composition for the treatment of steel to eliminate flaws and defects in the steel comprising a mixture of sodium carbonate, calcium fluoride and at least one from the group consisting of stearic acid and commercial stearin.

References Cited UNITED STATES PATENTS 472,422 4/1892 Alzugaray -94 X 681,527 8/ 1901 Brabrook 164-74 1,677,420 7/ 1928 Woodman 75-53 1,850,381 3/1932 Code 75-40 1,947,735 2/ 1934 Popham 75-40 1,997,602 4/1935 Robinson 75-53 2,130,228 9/1938 Clarke 75-53 X 2,823,112 2/1958 Miller 75-94 3,258,328 6/1966 Goss et al 75-53 X 3,269,828 8/ 1966 Hale 164-56 L. DEWAYNE RUTLEDGE, Primary Examiner.

H. W. TARRING, Assistant Examiner. 

1. DISCLOSE, A COMPOSITION FOR THE TREATMENT OF STEEL TO ELIMINATE FLAWS AND DEFECTS IN THE STEEL COMPRISING A MIXTURE OF SODIUM CARBONATE, CALCIUM FLUORIDE AND A SAPONIFIABLE FATTY ACID CAPABLE OF REACTING WITH THE SODIUM CARBONATE AND CALCIUM FLUORIDE TO PRODUCE A FOAMY SLAG CAPABLE OF UNIFORMLY COVERING LIQUID STEEL. 